Forbes Formation


The Forbes Formation of the Sacramento Basin represents deposition in a southward prograding deep-sea fan system fed by a deltaic system. Migration of deltaic lobes and the associated deep-sea fan deposits result in a complex lateral and vertical distribution of sandstone bodies. The resulting fan system is not a well-defined, discrete fan, but a series of smaller fans, comprising a fan system.

The Forbes Formation can be subdivided regionally by two low-resistivity shale markers and can be further subdivided locally. Specific emphasis of the petrographic study was to determine the compositions of the sandstones, define the diagenetic sequence, and to relate cementation to variations in porosity and permeability. Concepts derived in the 3 examined fields were applied to the regional evaluation of reservoir potential.

The study covers over 1,139 square miles, within which 587 wells were correlated, and represents seven man-years of geologic research.

Study Highlights

  • Study Text and Figures
  • 4 Measured Outcrops Described
  • 5 Cores Described
  • 587 Study Wells
  • 76 Thinsections Examined
  • 3 Field Studies
  • 19 Regional and 6 Field Maps
  • 10 Regional and 8 Field Cross Sections

Location Map

Forbes Formation Study Map